I had some problems balancing a couple of props for my .61 Thunder Tiger engine. I've read the threads relating to prop balancing, but didn't find an answer to my specific (weird) problems. First, I have been using a magnetic balancer and been using the method described in the balancer instructions where I remove material from the heavy side prop tip. On a couple of props it seemed like I had to remove a lot of material. So I measured from the hole to each prop tip. The side where I had removed material was shorter by 1/8" (on an 11 x 8 size)! Is that normal? Is that a usable prop? It did seem to balance OK.

It seems that some of the balancing "challenges" have been because the hole is just not exactly in the center of the hub. I have been reaming the prop holes out to accommodate the .61 size shaft with a hand reamer (stepped from smaller to larger). Will the larger (reamed out) hole in the prop always be pretty much on the same center as the smaller, original hole? Are there any tricks that would ensure the reamed out hole is in the center? Thanks.

Wing-Ding

With the hand reamer the hole will not shift. So the hole must have been off-centered to begin with. Best way to tell if both side are equal is to mount the prop on the engine and place a steady object at the end of one side of the prop. Rotate 180 deg and witness any varience. The long side should be sanded down to produce equal lengths; then balance.

[I remove material from the heavy side prop tip.]

Are you removing material from the end of the blade? You should remove material from the FACE of the heavy blade, thus nor affecting length.

You can also add clear dope etc to the light blade.

jess

Bill Vargas, one of the top pylon racers in the country, is in my club and changed the way I handle props. First, use a tappered ream. The object is to get a fit that correctly centers the hole on the shaft. It need not be the same diameter all the way through the prop hub. Ream from each side and keep checking the fit.

The actual balancing is done with fingernail polish. It is inert to fuel. You add it to the light side of the blade, without changing the shape of the blade to any measurable degree. It may take a couple of coats if the prop is badly out of balance. This also has the added advantage of making the one side of the prop more visible when it is spinning. The cheap stuff works as well as the expensive stuff and is avaliable in a wild range of colors.

One of the hobby product makers (I forgot which) seems to have noticed some off-center drilling done in wood props. They now produce a prop balancer where you mount the prop in a special drill guide and mount that guide in tha balancer rig. You shift the whole prop in the guide to achieve balance. Clamp firmly (recheck balance to be sure it didn't shift)... and drill the new shaft hole.

I prefer to use clear spray urethane instead of physically working on the prop when balancing.
The magnetic balancer should be the best method of finding the light blade.. add the paint to that side.
As for off-center holes, your 1/8" is extreme.
Best to get both blades to the same length from the center, then balance.
A hand-reamer of the stepped type if it's not forced will center itself in the existing hole, then slowly work it to the next size up.
A tapered reamer will do the same job, but be careful with any tilt when going thru.
The hole in the prop itself need only the size of the shaft diameter at one place for a good fit; the stepped reamer is better in this respect.
The front and rear support washer do the actual gripping of the prop to the motor.
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ps: on molded props, I take the flash off the leading edges with some fine grit sandpaper, just to have a more airfoilish shape at the important side of the prop.
pps: I've learned to NOT flip a molded prop by hand, and use a starter. Working the trailing edge to a less painful shape isn't worth the effort.

The APC sharp TE of the prop blade is ON PURPOSE. Its part of the blade design. Sanding that off is not a good idea.

You can learn to handle the prop without ever touching the TE... and can even hand start without touching the prop's TE by back-flipping...which is much safer than hand starting by flipping forward, running your fingers over the sharp TE... (safe hand starting is an art that must be LEARNED or you are better off to just keep using the electric engine grinder.)

If you are going to hand-flip an APC it is OK to wear a heavy leather glove. Also, if you are not using a glove, flip by putting your finger tip against the prop face rather than around the trailing edge. I forgot a while back and can show you a nicely healed scar as a result.

Jim

FHHuber is right about back fliping a prop. Its an art. Took me a long time to master it. You really need to know you engine and how much and when to choke it. But it is cool and safe. I grab the prop as close to the spinner as I can and just snap my fingers. Starts everytime.